The present invention relates generally to metal working and more specifically to rotary cutting tools.
The invention can find most utility when applied for machining both outside and inside cylindrical surfaces, as well as intricately shaped surfaces and planes of workpieces made from hard-to-machine ductile metals characterized by formation of continuous chips.
An indispensable prerequisite for practical realization of the process of rotary cutting featured by high machining speeds, is a successful solution of the chip breaking problem. The heretofore known chip breaking methods applied in rotary cutting can be classified into two groups. There belongs to the first group the method of making notches, grooves or checks on the tool cutting face; said method though capable of stable chip breaking is, however, subjected to some disadvantages. First the provision of notches, grooves, and the like reduces the number of feasible tool regrindings and hence its total service life; secondly, discontinuity of the cutting blade impairs the quality of surface finish.
Provision of attached stationary knives for chip breaking within the zone of the chip contact with the tool face is instrumental in chip breaking; however, interaction of the chip with the cutting element and the attached stationary knife results in heavy impact loads imposed upon the both of them at the place of their contact with the chip, so that cyclic stresses are liable to arise on the cutting blades thereof, eventuating in their premature wear and chipping-off which to a great extent affects adversely tool endurance and the quality of machined surface finish.
There pertains to the second group of chip-breaking methods the one providing for chip thickness variation in the course of metal cutting process by virtue of an eccentric tool cutting lip. When cutting with such tools their top (i.e., the point on the cutting lip corresponding to a maximum depth of tool penetration into the material being machined) which imparts the final shape to the machined surface, is displaced with respect to the workpiece axis, and chip breaking occurs due to radial runout of the eccentric tool cutting lip.
The result is an altered actual cutting depth and affected quality and accuracy of machining.
One more rotary cutting tool is known to comprise the body accommodating the spindle carrying the cutting element shaped as a solid of revolution, viz., cup-shaped, and the chip breaker knife.
The knife is set in the spindle bore and held by a nut. The knife blade is located as close as possible to the taper face of the cutting element and is spaced apart from the cutting lip thereof at a distance not exceeding the zone of chip contact with the tool surface.
The knife is made as an L-shaped member tightly forced against the taper flank of the cutting element.
When the spindle is running the cutting element removes the chip and the knife, in turn, periodically cuts the chip into portions.
A disadvantage inherent in the above tool construction resides in the fact that impact loads cause high cyclic stresses, whereby the cutting lips of both the cutting element and the chip breaker knife are liable to badly crumble out at the points of their contact.
As a result, the endurance of the cutting element and the chip breaker knife is adversely affected and the quality of surface finish is impaired.